Rebuilding a 1973 2.4T Engine
 

The engine was partly overhauled with 84mm piston & cylinders supplied by AA(part number 00891184S).

The engine runs on ZENITH cards.

These pistons differed from the originals in that they were of dome shape head. I have enquired at the time if these were possible to be fitted, bearing in mind the increase their shape would have on the compression, and your response was that yes they can be fitted.

The engine overhaul was completed with value and ignition timing settings followed from manufacturers 911T technical data.

When driving the vehicle particularly after the engine has warmed up there is considerable pre-ignition, "pinking". Different grades of petrol have been tried, and also different ignition timing settings alas to no avail.

I would appreciate your views on the matter whether perhaps with the effect to compression and subsequent temperature increases of these dome pistons other modifications to the engine were necessary, in order to accommodate these.

Pre ignition or "pinging" is mostly caused by either too much ignition advance...or too low an octane in the fuel (for the compression factor of the engine).
So...the fixes are....lower the compression (expensive)
...retart the timing (easy..but might lose some power...and build more heat in the engine)
..#3...buy better gas (petrol)...
Sometimes a little fatter on the carbs might help too (richer).
Good luck.
Bob

I have tried everything, it seems that I have to go back to Original MAHLE pistons and cylinders to solve my problem

Part number implies that these pistons are for 911 S: 008 911(model)84(cyl bore)S(version)

Try to retard timing by 3-4 degrees and use premium fuel and enrichen the mixture a bit. You should check the mixture with WBo2 meter so it stays 12.6-13.0 at WOT.

Here's the link to them, it clearly states that they are high compression: http://aapistons.com/index.php?main_page=product_info&cPath=15_16_11&pr oducts_id=14